Centralized traffic controlling system for railroads



Nov. 8', 1949 w. M. BARKER 2,487,412

CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS 2 Sheets-Sheet 1 555mm 455 88 x:

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Patented Nov. 8, 1949 CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS William M. Barker, Greece, N. Y.,

General Railway Signal Company,

assignor to Rochester,

Application October 24, 1947, Serial No. 181,820

9 Claims.

This invention relates to communication systems for railroads, and it more particularly pertains to a centralized trafiic control system of the shunt type used in combination with selector calling wherein a single pair of line wires serves the dual purpose of being used both for code communication in the centralized trafiic control system and for telephonic communication where selector calling is employed.

The centralized traffic control system, conveniently called a C'I'C system, of the general'character disclosed in the patent to Hailes et al. No. 2,399,734 dated May '7, 1946, for example, provides for the communication of switch and signal controls and the like from the control office to respective field stations, and provides for the communication from the respective field stations to the control ofiice of indications of the positions of respective devices. Such communication is accomplished over a single pair of line wires, the integrity of which is maintained at all time, and thus these wires can be used for telephone communication between the control office and respective selected field stations.

The relatively high frequency voice current at relatively low power of the telephonic part of the system can readily be segregated from the CTC part of the system by suitable band-pass filter means, and thus the telephone communication and GT facilities can be used simultaneously The selector calling sys' without interference. tern, however, operates by transmission of pulses at a relatively low frequency, and in order to prevent interference between the selector system and the CTC system, it is desirable that only one of such systems be rendered active at a time, or that distinctive conditions of line circuit energization for the respective CTC and selector systems be employed as is disclosed in my prior Patent No.

2,422,519 dated June 17, 1947. This problem of allowing time becomes a more difficult problem when it is considered that the transmission of a selector cycle from the control office and the transmission of an indication cycle from a field station may be initiated simultaneously. The interruption of an indication cycle which has once been initiated'at a field station may cause the loss of the indications that were to have been transmitted. In other words, an incomplete CTC cycle would rethe transmission of but one cycle at a sult and this is considered in a CTC system as a failure of some part of the communication system apparatus at the field station transmitting, and. because such failure may cause monopolization oi the line circuit it is provided as in the above mentioned Hailes et al. patent that the cycle start is cancelled, and the initiation of another indication cycle at that station can be effected only by another change in a device to have its position indicated at the control ofiice.

An object of the present invention is to'so coordinate a selector calling system with a CTC system of the character described in the above mentioned Hailes et al. patent that there is no possibility of loss of an indication cycle because of the transmission of a selector cycle, even under simultaneous start conditions of transmission of both selector and indication cycles.

Another object. of the present invention is to give the transmission of selector codes preference over the transmission of some indicationsbut not over the transmission of others. That is, in the above mentioned Hailes et al. patent, indication cycles are transmitted according to groups, one cycle from each station in the group until an indication has been transmitted from each station in that group. Each group comprises all stations having indications to transmit at a time when there is a relatively long period of rest of the system. It is thus provided that a selector cycle has preference over an indication cycle of a second group, but the selector cycle cannot break into any one group of indication cycles.

Another object of the present invention by making use of inductive coupling of the selector transmitter at the control ofiice to the line circuit is to cause the length of the selector pulses to be sufficient to operate a conventional electromechanical selector receiver at each field station but insuiiicient to simulate OTC pulses and thus erroneously act upon the CTC communication apparatus.

Another object of the present invention is to permit the designation of a selector code for transmission at any time, and to store such designated code until the CTC system is available for its communication to the respective field stations.

Other objects, purposes characteristic features of the present invention will be in part obvious from the accompanying drawings and in part pointed out as the description progresses Reference is made to the accompanying drawings in which similar reference characters are used to designate corresponding parts of this disclosure and th above mentioned Hailes et al. patent; in which the symbols and are used to indicate connections to respective positive and negative terminals of suitable batteries or other sources of direct current; and in which:

Fig. 1 illustrates schematicaliy the organization 3 of apparatus at a control office for the transmission of CTC and selector codes respectively;

Fig. 2 illustrates CTC and selector apparatus at a plurality of field stations; and,

Fig. 3 illustrates by sequence charts the sequence of operation of the respective relays at the control ofiice during a selector cycle transmission.

The control ofiice appartus comprises the apparatus disclosed in Figs. 1A, 2A, 2B, and 2C of the above mentioned Hailes et a1. patent, together with a selector transmitter which can be provided as disclosed, for example, in the patent to J. C. Field No. 1,976,548 dated October 9, 1934.

In addition to the above mentioned apparatus employed at the control ofiice, selector relays SS, SP and SPP (see Fig. 1) are'employed in governing the initiation of the respective selector cycles. Some of the CTC system relays have their control circuits modified so as to be controlled by one or more of the relays SS, SP and SPP.

Inasmuch as the present invention is more particularly concerned with means including the relays SS, SP and SPP for governing the order of superiority of respective control, selector, and indication cycles, it has been considered unnecessary for the understanding and practice of the present invention to disclose other than the circuits of the system that differ from circuits disclosed in the above mentioned patents, as reference can be made to those patents for a disclosure of parts of the system that are old in the art. However, as a matter of facilitating the understanding of how this invention ties in with the above mentioned patents, certain of the circuits of such patents have been shown, and these circuits can be readily identified with the respective prior disclosures because of use of corresponding reference characters.

Similarly the apparatus at each field station is assumed to comprise complete CTC and selector station apparatus, the CTC apparatus corresponding to that disclosed in the Hailes et al. patent, and the selector apparatus corresponding to that disclosed in the Field patent. Certain of the circuits from these patents have been shown in Fig. 2 as a matter of facilitating the understanding of the mode of operation of the system under certain conditions to be encountered in practice such, for example, as under conditions where the start of an indication cycle at a field station is simultaneous with the start of a selector station at the control oflice.

Having thus described the apparatus employed in one embodiment of the present invention, the circuit organization will be hereinafter considered together with various typical operating conditions to be encountered in practice.

Operation The apparatus according to the present invention is normally at rest in that the line circuit is steadily energized with a particular polarity characteristic of the rest condition of the system, and thereby provides efiectively a permission condition of energization of the line circuit which allows a field station to initiate an indication cycle in response to a change in a device at that field station to be indicated at the control office.

From this period of rest, either a control or an indication cycle can be initiated, and upon such initiation, the system enters a conditioning period which is called an off period if the control office is transmitting or a shunt period if a field station is transmitting. The conditioning period is short or long dependent upon whether the field or the control office starts the cycle respectively. By the conditioning period being made long because of a start at the control oflice, the control office can overcome a simultaneous field station start so as to allow the control office to maintain control of the line for the transmission of a control cycle.

Following the last on period of a control cycle, or non-shunt period of an indication cycle, the system enters a clear-cut period during which the apparatus at the control office and at the various field-stations is restored so as to condition the system for the initiation of another cycle of operation. Following the clearout period at the end of a cycle of operation the system enters a period of rest from which it can be initiated into another cycle of operation.

It is similarly provided in response to designation of a selector code for transmission to the field that the system enters a selector cycle of operation from a period of rest during which there is a conditioning period of substantial length as compared to the length of the conditioning periods during the respective control and indication cycles, and after transmission of the selector pulses, the system enters a relatively short clear-out period during which the selector and CTC apparatus is restored to condition the system for the transmission during another cycle of operation.

When the system is at rest, the line circuit is maintained energized with what is conveniently termed a positive polarity to allow any field station to register at the control oifice the start of an indication cycle by the application of a shunt across the line wires at that field station. With reference to Fig. 1, the positive terminal of the line control battery CB is illustrated as being connected through limiting resistor RI, back contact 23 of relay C, front contact 24 of relay OR, back contact 25 of relay CF, back contacts 600 and GM of relays SS and SPP re- .spectively connected in multiple and low pass filter windings 26 and 21, to the line wire 22. The negative terminal of the control battery CB is connected to the line circuit through the primary winding 29 of the impulse transformer 30, back contact 3| of relay 0, back contact 32 of relay CF, back contacts 602 and 603 of relays SS and SPP respectively connected in multiple, and. low pass filter windings 34 and 33, to the line wire 28.

With reference to Fig. 2, the energization of the line wires 22 and 28 with a positive polarity as described energizes the line relay 2F with a polarity to actuate its contacts to their righthand positions by ,a circuit extending from wire 22 including low pass filter windings 35 and 36, back contact 31 of relay 2L0 upper winding of relay 2F, resistor 38 and capacitator 39 connected in multiple, lower winding of relay back contact 40 of relay 2L0 and windings ll and 42 of the low pass filter, to the line Wire 28. With the relay 2F energized by this polarity to actuate its contacts to their right-hand positions, the closure of contact 2M in its right-hand position conditions a circuit for the relay ZCHP so that such relay can be picked up to initiate an indication cycle in response to the dropping away of the change relay 20H due to the opening of its stick circuit by the shifting of the contact 46 or 45 of one of the track relays TR or ATR.

' pulse transformer 30-.

Transmission during selector cycle 7 To consider the mode of operation and circuit organization for the transmission of a, selector cycle, it will be assumed that the transmission of. a selector cycle. is initiated at a time when the system is at rest and the line circuit is energized with a positive polarity. To. initiate, the selector cycle the operator designates the code. for transmission by the actuation of respective buttons SPB, (only one of which is shown in Fig. 1). The actuation of these buttons is efiective as described in the above mentioned Field patent to select. the selector code characters to be transmitted. The buttons SPB when actuated are locked in their actuated positions until they are released automaticaliy by the actuation of other buttons subsequent to the completion of the selector cycle.

It is thus provided that in response to the actuation of a button SPB for starting the transmission of a selector code, the relay 86 is picked up, and the picking up of that relayby the closing of front. contact. 604 applies energy of negative polarity to the wire 94. Assuming the system to be at rest, the relay SS is picked up in response to the picking. up of relay 86 by the energization of a'circuit extending from including back "contact 605 of relay LOT, winding of relay SS,

back contact 686 of relay SP, wire 94, front contact 6'04 of relay 86, and other circuit selections 'as shown in the above mentioned Field patent,

The picking up of relay SS by the closing of front contacts 600 and 602' applies a shunt across the line circuit, and across the control battery CB, through the winding 636 of the selector coupling transformer BOT. The shunting of the line circuit, by drawing anincreased amount of current through the primary winding 29- of the impulse transformer 30, provides for the energization of the upper winding of relay F with a polarity to actuate the contacts of the relay F to their left-hand positions. The circuit for the upper winding of relay F under such conditions extends from the right-hand terminal of the. secondary winding 356 of the transformer 30, including the upper winding of relay F, back contact 35'! of relay LV, back contact 358 of relay C, and back contact 359-01? relay SC, to-th'e left-hand terminal of the secondary winding 356- of the'i'm- It is thus provided that the shunting of the line wires 22 and 28 by the picking up of the relay SS at the beginning of a selector cycle is efiecti've to initiate a conditioning period comparable to the manner in which a conditioning period'is initiated at the beginning; of an indication cycle where a shunt is applied across the linewires 22 and 28 at. a field station. Thus in comparing the sequence of operations at the control oflice at the beginning of an indication cycle as shown in Fig. 8A of the above mentioned Hailes' et. a1. patent with the sequence chart according, to- Fig. 3 of this disclosure, it will be apparent that the shifting of the contacts of, the relay- F to their lett-hand positions is effectiveto pickupthe relays LET, LOT.

- is picked up in response tothe picking up of relay CF, and the relays SA, SB and SC-are-succes-.

si-vely picked up, the picking'up of relay SA bein effective to cause the picking upof. relay- E;

The; relay LET'i-s slightly quicker in pickingv up than, the relay CF so: that the: secondary winding .355 or the impulse transformer 3:0; isshunted byrelay C, front contact a circuit including back contact GM of, relay: SB and front contact 599-: of relay LET before the linecircuit is opened by: the. pole: changing of the battery CB upon the shifting of contacts 25 and 32 of relay CF. It is thus: provided that the reversal of the polarity of energization. of the line circuit cannot act upon the relay F through the impulse transformer 30. Subsequent to the picking up. of relay CF, the positive terminal of the battery CB, rather than being connected to the line wire '22 as has been described for the positive ener-gization of the line circuit, is connected tov the line wire 28' through back contact 23 of 32 of relay CF, back contact 603 of relay SPP and low-pass filter windings 34 and 33. The negative terminal of the battery GB is connected through the primary winding 29; of the impulse transformer 30, back contact. 31 of relay C, front contact 25 of relay CF, back contact tel of relay SPP and low-pass filter windings 26 and 21, to the line wire 22.

The picking up of relay LOT near the; beginning of the conditioning period in response to the shifting of the relay F is effective to open the circuit for the relay SS at back contact 605, and thus the relay SS is dropped away toremove the shunt across the line circuit and leave the line circuit conditioned with energization of a negative polarity, The energization of the line circuit with a negative polarity under such conditions acts as a lock-out at all field stations by the actuation of the line relays F at those stations to a position to prevent the initiationv of an indication cycle. It is thus provided that there can be no field starts initiated subsequent to. the negative energization of the line circuit at the beginning of the conditioning period.

The picking up of relay SC during. the conditioning period causes the picking up of the selecrelay SPP through back contact N3. of the selector start relay SS.

By the picking up ofv relay SPP, the backv contacts 601 and 603 of that relay in the line cirunit are opened, but because of the closure. of the back contacts 608 and 60.2 of relay SS, in multiple with these contacts, the line circuit. remains connected to the control battery CB. untilthe. relay SS is again picked up at the end of the conditioning period. The resistor 61.4 is connected in multiple with the Winding of the: relay SPP to cause that relay to be sufficiently slow in dropping away as to allow for the pick up time of the. relay SS and the time of shifting of contact .613 of relay SS whenthat relay is picked. up to establish a stick circuit so as to maintain the relay SPP picked up throughout the transmission of relay, F with a. polarity to actuate the. contacts: of that relay to. their right hand; positions.

contacts 483 of relay SA, front contact 484 of 'relay SC, back contact 485 of relay SB, and the center winding of relay F, to

Upon the shifting of the contacts of relay F to their left-hand positions, the circuit for the energization of relay LOT is opened, and the dropping away of that relay by the closure of back contact 665 closes a portion of the circuit for the selector start relay SS, but such relay cannot be picked up until the relay SP is dropped away to close back contact 666; The shifting of the contacts of relay F is also efiective to cause the picking up of relay OR, and the picking up of relay OR, in turn, provides for the successive dropping away of the relays SC and SP. The

circuit for the relay SC is opened at back contact N5 of relay OR upon the picking up of that relay, the front contact 6I6 of relay SB being open at that time. The relay SP is dropped away in response to the dropping away of relay SC by the opening of front contact 609.

Upon the dropping away of relay SP, the closure of back contact 606 of that relay in the circuit for the relay SS causes the relay SS to be picked up for a second time by the energization of a circuit which has been described. The picking up of the relay SS at this time, because of the relay SPP being picked up, causes the connection of the selector transmitter to the input of the coupling transformer 60? through the resistor RI which is shunted by the condenser Cl. Such energization of the input to the coupling transformer is accomplished in accordance with the energization of the line relay 14 by a circuit extending from including the winding of relay 14, front contact 6!! of relay SS, front contact N8 of relay SPP, wire 94, front contact 604 of relay 86 and selections as required in the selector transmitter, to It is thus provided that by the energization of the relay M, the control battery CB is connected to the primary winding 6l9 of the coupling transformer 60'! through pole changing contacts 620 and 62! of the pole changer relay 15, a, suitable low pass filter 622, the contacts 623 and 624 of the line relay l4, and the resistor R! and condenser Cl connected in multiple.

Having thus provided connections for the output of the selector transmitter, the operating mechanism of the selector is rendered active by the closure of a circuit for the synchronous motor I08 which drives a segment brush in a manner to scan the contact segments and thus provide selective energization for the pole changing relay 15 to govern the transmission of selector code pulses according to the code designated by the actuation of the selector code push buttons SPB. The motor N38 is initiated by a circuit extending from one terminal designated as BX of a suitable alternating current power supply, including front contact 625 of relay SPP, front contact 626 of relay SS, and motor 08, to the opposite terminal of the alternating current supply designated as NX. The pole changing relay'l5 is pulsed in accordance with the usual practice for selector transmitters as is disclosed in the above mentioned Field patent to transmit a selector code comprising three groups of pulses, such pulses being of alternate polarity as provided by the selective energization and deenergization of the pole changing relay T5.

The short oppositely poled pulses which are induced in the secondary winding 636 of the transformer 60! are applied across the line wires transmission of indications.

22 and 28 through front contacts 600 and 602 of the relay SS and through the low-pass filter windings 26, 21, 33 and 34. Because of the relay SPP being in a picked up position prior to the picking up of the relay SS a second time during the conditioning period ofthe selector cycle, the back contacts 69! and 603 of relay SPP are open so that the opening of back contacts 600 and 602 of relay SS disconnects the CTC transmitting apparatus from the line wires 22 and 28, thus providing that the only energization applied to such line wires during a selector cycle is that which is induced in the secondary winding 636 of the transformer 601.

According to the above mentioned Field patent, when a selector cycle is completed, a relay B4 of that patent is picked up, and the picking up of that relay causes the interruption of the circuit for the motor I08. For the purpose of simplification of the disclosure of the present, invention, this selection to deenergize the motor at the end of each selector cycle is merely indicated by the letter X in the motor circuit. By the picking up of this relay 84 as disclosed in the Field patent, the circuit for relay 86 is opened and thus that relay is dropped away, even though the keys SPB are maintained mechanically locked in their actuated positions until the subsequent actuation of another key. The dropping away of relay 86, in turn, is effective by the opening of its front contact 604 to deenergize the selector line control relay M and also the selector start relay SS. Deenergization of relay 14 by opening front contacts 623 and 624 disconnects the battery CB from the transformer 601, and the dropping away of relay SS, by the opening of front contact 626 deenergizes the motor I08. The opening of front contact 6| 3 causes the dropping away of the relay SPP to complete the restoration to normal of the apparatus associated with the transmission of a selector cycle.

Because of the relay OR having been picked up near the end of the conditioning period, the dropping away of the relay SS after transmission of selector pulses has been completed, by the shifting of contacts E566 and 662 in the line circuit, disconnects :the secondary Winding 636 of the coupling transformer 60'! from the line circuit and reconnects the line wires 22 and 28 to the control battery CB for energization of the line circuit with a positive polarity corresponding to the polarity which has been described as being applied ltO the line circuit during a period of rest.

Reception during selector cycle It has been described that upon intiation of a selector cycle the line circuit is pole changed and energized with a negative polarity for the purpose oflocking out any subsequent field station starts of indication cycles. With reference to Fig. 2, this is accomplished by the shifting of the contacts of rela 2]? to their left-hand positions in response to the negative energization of the line circuit, and in accordance therewith, the opening of contact 2| 4 in its right-hand position is effective to prevent the picking up of the relay ZCHP in response to a change calling for the That is, if there is a shifting in the position of either contact 45 or contact 46 of the respective relays ATR and TR, the relay 20H is dropped away because of the opening of its stick circuit, and the dropping away of relay ZCH, by the closure of back contact 336,

' conditions the relay ZCHP so that it can be picked 9 vided that the line circuit is energized with positive polarity.

It is thus provided that the conditioning at a field station at the beginning of a selector cycle is effective in a manner corresponding to that described, and specifically illustrated by the sequence chart of Fig. 7A, in the above mentioned Hailes et al. patent relative to the mode of operation Of apparatus at a field station that does not have indications to transmit during the conditioning period of an indication cycle. According to the sequence of operation of the relays, upon the shifting of the polarity of the line circuit, the line relay 2F (see Fig. 2) has its contacts actuated to their left hand positions, and by the opening of contact 48 of that relay, the relay 2FR is dropped away, and upon the droppin away of relay 2FR, the closure of back contact 2I3 provides for the picking up of the cycle distribution relay 2CD. With relay 2CD picked up, the opening of back contact 33 3 in the circuit for relay 2CHP further prevents the picking up of relay ZCI-IP during the selector cycle. It is therefore provided that :by the opening of back contact 334 of relay 2CD during the conditioning period and maintaining of that contact open throughout the selector cycle, it is insured that the relay 2CHP cannot be picked up until the cycle is completed, even though the contact 214 of the relay 215' is intermittently closed in its right-hand position for short periods of time because of the relay 2F following the selector code pulses of both polarities during the transmission of the selector code.

According to the normal mode of operation of the CTC system as described in the Hailes er, a1. patent the relay HR is maintained dropped away throughout the cycle and thus holds energy on I the relay 2CD. The conditions during the selector cycle differ, however, from those during a control or an indication cycle at field station 2F in that the pulses of the selector code may not be of sufficient duration or .of a sufficient frequency to maintain the relays ZSA and 28B steadily picked up throughout the selector cycle. Thus, because of its being possible that relay 283 may be at times picked up and at times dropped away during the selector cycle, the circuit for the relay ZFR is intermittently closed at back contact 49 of relay ZSB when the contact 48 of relay 2F is closed in its right-hand position. Therefore because of the relay ZFR being intermittently picked up, the relay 2CD is only intermittently energized by the closure of back contact 213. The stick circuit for the relay 2CD, however, which is dependent upon back contact 500 of relay "ZFA is also intermittently closed because the relay 2FA is.

onl at times energized in response \to the pulsing of the relay 2F. It is therefore provided that the relay 2CD is maintained steadil picked up throughout the selector cycle by the combined intermittent application of energy to that relay by the back contact 213 of relay 2FR and the back contact 50!! of relay 2FA. In this manner the relay 2CD is maintained steadily picked up throughout the selector cycle, and therefore the pick up circuit for the relay ZCI-IP is maintained steadily opened at back contact 334 to prevent the picking up of that relay during the selector cycle.

The selector [66 is directly connected across the line wires 22 and 28, and such selector goyerns the ringing of the bell BL in accordance with the reception of code characters corresponding to the predetermined code assigned to selector station No. 2. The code to which the bell is responsive is determined by the location of pins in a code wheel in a manner well known to those familiar with the art. It is thus provided that the reception of a selector code corresponding to that assigned to the selector station No. 2 is effective by the actuation of the contact finger 621 to apply energy to the bell BL for a predetermined length of time. It is preferable that the bell circuit be coupled back into the line circuit through suitable capacitors for the purpose of answer-back so that the operator at the control office will be informed that the call has been completed. Such answer-back circuit has not been shown for the purpose of simplification of disclosure of this embodiment of the present invention as this particular feature is well known to those skilled in the art.

At the end of the selector cycle the system enters a clear-cut period at the respective field stations during which the CTC communication apparatus is restored to its normal condition in a manner similar to that which is fully disclosed in the above mentioned Hailes et a1. patent.

Simultaneous selector and indication cycle starts Upon consideration of the mode of operation during a selector cycle as it has been described, it will be noted that the line circuit is momenttarily shunted by the relay SS at the beginning of the cycle and then'the shunt at the control (mice is removed for a period of time during the conditioning period. By such mode of operation, it is provided that in case there is a simultaneous start of a selector cycle and an indication cycle whereby the shunting of the line circuit at the field station is rendered effective substantially at the same time that the relay SS is picked up for initiation of the selector cycle, the line remains shunted subsequent to the dropping away of the relay ,SS at the beginning of the cycle for the initiation of an indication cycle.

According to the mode of operation during a selector cycle as it has been described, the relay S S (see Fig. 1) is dropped away near the beginning of the conditioning period at a time when the secondary winding 356 of the impulse transformer .30 is shunted by the contacts 698 and 599 of relays SB and LET respectively. It is therefore provided that the dropping away of the relay SS at this time and the removal of the shunt across the line circuit does not affect the line relay F because of the secondary winding :356 of the impulse transformer 30 being shunted. If, on the other hand, the line circuit is shunted in the field for the conditioning of an indication cycle, because of the timing of the apparatus at the field station, the line shunt is not removed until the relay SB at the control office has been picked up to open the shunt across the winding 355 of the impulse transformer 30 at back contact 608 and thus render the line relay F at the control oflice responsive to the removal of the line shunt at the field station whichhas initiated the indication cycle.

It is therefore provided that in case an indication cycle is initiated, the conditioning period is terminated in the usual manner by the field station transmitting before the relays LET, SA, SB and SC have had time to be dropped away Inasmuch as the relay SC at the control ofiice c n o b d o p way du in the cond tion ng period, the relay SP is maintained picked up by its circuit closed at front contact 509 of relay .SC. With relay SP picked up, the circuit for th elector s rt e ay .SS is he d open at back cone tact 606, thus preventing the picking up of this relay until after the indication cycle is transmitted in the usual manner. It is therefore provided that in case a relay CI-IP at a field station is picked up prior to or substantially the same'time as the shifting of the polarity of the line circuit by the initiation of a selector cycle, the indication cycle initiated by such relay CHP is transmitted in preference to the selector cycle.

Assuming an indication start to have overruled a selector start as described above, when the indication cycle is completed, the relay SC is the last relay to be dropped away at the control office, such relay being dropped away during the period of rest which follows the clear-out period. Subsequent to the dropping away of the relay SC, the relaySP is dropped away because of the opening of its circuit at front contact 609 of relay SC, and the dropping away of that relay, by closing the pick up circuit for relay SS at back contact 606, renders the start of a selector cycle effective.

However, upon starting the selector cycle following the transmission of an indication cycle, the selector cycle start may again be rendered inferior to an indication cycle start if some other field station has its relay CHP picked up for the start of an indication cycle. It is thus provided in this way that the selector start will not be able to rule until the relay CHP at each of the field stations is dropped away. At such time, the system must enter a relatively long period of rest, as far as the transmission of indication cycles is concerned, until the cycle distribution relay CD at each field station has had time to drop away and condition the associated relay CHP as by the closure of back contact 334 in the pick up circuit of relay ZCHP, so that such relay can be picked up to make that station a party to another group of indication stations having indications to transmit.

Because of the time required for the dropping away of the relays CD under such conditions in order to initiate another group of indication cycles, assuming that there has been a selector cycle previously designated, the positive energization of the line circuit during the period of rest is terminated prior to the dropping away of the relays CD, and thus the energization of the line circuit with a negative polarity because of the selector cycle start prevents the picking up of any relay CHP to initiate an indication cycle at any of the field stations wherein a change relay CH has been dropped away until the selector cycle has been completed. It has been pointed out when considering the mode of operation of the system during the transmission of a selector cycle that the negative energization of the line circuit is effective during the conditioning period to lock out the start from any of the field stations, and subsequent to the conditioning period the relay CD at each field station is efiective to prevent the picking up of the relay CHP at that station. It is thus established that the transmission of a selector cycle can be rendered effective only when the relays CHP at the respective field stations are all dropped away, and that the transmission of a selector cycle has preference over the initiation of a second group of indication cycles but not over a first group when such first group is in progress, or is simultaneously initiated at the time when the selector cycle is started. For a more specific description of the cycle distribution system of grouping stations as they have indication starts, reference is to be made to the descrip- 7 SC which is picked up both for control and indi-.

Selector start designated during CTC cycle It will be apparent from the description as it has been set forth that the relays SP and SPP are picked up during each CTC cycle because the,

relay SP is dependent upon the slow acting relay cation cycles, and the relay SPP is picked up in response to the picking upof the relay SP when the selector start relay SS is dropped away. Because of the back contact 606 of relay SP being included in the pick up circuit of the relay SS, it is thus provided that the relay SS cannotbe picked up to shunt the line circuit during a CTC cycle for either the transmission of controls or indications. relay to drop away at the control office during either a control or an indication cycle as is shown in the sequence charts of the above mentioned Hailes et al. patent, it is provided that Where a selector. start has been designated during a CTC cycle, the picking up of the selector start relay SS to set the selector transmitter into operation is effective only after the slow dropping away relay SP has had time to drop away and close back contact 696 in the circuit for the relay SS subsequent to the dropping away of relay SC and the opening of. the circuit for relay SP at front contact 639.

Because of the system being already in a period of rest wherein the line circuit is energized with a positive polarity by the time that relay SC is dropped away, and because of the slow drop away characteristics of the relay SP, there is a sufiicient time interval between the time of the positive energization of the line circuit at the end .of a cycle, and the time when the relay SS could be picked up in response to the dropping away of relay SP to allow a field station start of an indication cycle to have been initiated provided that a relay CHP were picked up at any field station. In case there is a relay CHP picked up at any field station under these conditions, the relay LOT is picked up in response tothe indication cycle start, and by the picking up of that relay, the selectorstart relay SS is prevented from picking up by the opening of its circuit at back contact 605 of relay LOT, or the relay SS is dropped awayif it already has been picked up.

If it is assumed that there are no relays CHP picked up at any of the field stations, and the initiation of a selector cycle has been designated during a CTC cycle, the relay SS is picked up in response to the dropping away of relay SP by the energization of a circuit as has been described, and upon the picking up of that relay, the relay SC is picked up by the energization of a circuit extending from including back contact 628 of relay SB, back contact 629 of relay CF, back contact 63d] of relay LCS, front contact 63| of relay SS, frontcontact 632 of relay SPP, and winding of relay SC, to The relay SPP, by being maintained picked up at this time disconnects the battery CB and the impulse transformer 39 from the line circuit so as to prevent the movement of relay F when the selector transformer GM is connected across the line. Thus the pole changing of the line circuit by the picking up of the relays CF, and other relay operations which have been described as being effective during the conditioning period of a selector cycle are not required, and the transmission of selector pulses is rendered effective immediately in response to the pick up Inasmuch as the relay SC is the last of the relay SSattheend-of the c l Ccycle The intermittent application of positive pulses to the line circuit during selector code transmission .is ineiiecti-ve to simulate a period of rest, :and thus therecan-be no relay C-I-IP picked up atany field station during the transmission of selector pulses.

When the transmission of the selector'pulses as rendered efiec'tive by the pulsing of the contacts 620 and 62i of the relay l5 iscompleted, therelay 86 is-dropped away as has been described,land the dropping away :of that relay by opening its .front contact L604 causes the deenergization of the :line relay 1-4 and the dropping away of .the relay SS.

Relay SS in droppingawaycpens the circuit for the synchronous motor 168 at front contact 6-25.. 'lhe motor 1118 has, however, been already stopped in a manner that has been heretofore described with reference to the above mentioned Field patent. The dropping away of relay SS under such conditions opens the circuit for the relay SC at front contact 63! to cause that relay to .be dropped away. The relay SB is dropped away at that time so that .a pick up circuit for the relay SCis .openat front contact BIG and the relay OR is picked up so that the back contact 16! 5 is open. The :relay .SP is .picked up in response to the closure of back contact 61 I of relay SS, but upon the dropping :away of relay SC, the relay SP becomes dropped away because of the opening of its circuit at front contact 609 of relay SC. Upon the dropping away of the relay SP, the relay SPP lbecomes deenergizedibythe opening of its circuit at front contact 161.2, and the dropping away of this relay completes the restoration of the parts of the system associated-with the communication .of the selector code to :the field stations.

aConsider'ingthe general.accomplishmentsof the organization as it has been described, it is desirable to permit the transmission of a selector cycle only when the relay CHP at each field startion is dropped away because the reception of the selector pulse might cause the actuation of the stepper relays to the extent of permitting the restoration of a relay CHP without having first transmitted an indication cycle. Inasmuch as an associated relay CD is required to be dropped away in order to pick up a relay CHP during a .cycle, it is provided by theme of short selector pulses that sufiicient'energy is applied to the relay CD at each field station during a selector cycle to maintain it picked up throughout that cycle.

.In accordance with the desirability of allowing any field station to be superior to a selector cycle .start when its relay CHP is picked up, it is providedthat a relatively long period of rest is retq-uired in order-to render a selector cycle superior to an indication cycle. In other words, there is :but one indication cycle transmitted for each field .station in a group of stations having their re- ;lays CHP picked up at the time the selector code is designated for transmission, and the selector cycle is transmitted at the end of that group :of indication cycles where there is a longer period of :rest, but before the period of rest has been long enough to allow relays CD to be dropped away and associated relays CHP to bev picked up to form another group of stations having indications to transmit.

The operation of the selectors at the respective field stations is prevented during .CTC cycles of operation because the impulses transmitted during the CTC cycles are .of the same polarity, and a selector .is dependent for its operation upon the reception of pulses of alternate polarity. In other Words, the selectors are responsive step 'by step such systems being normally only as the pulses received are of first one polarity and then the other. It is thus provided that although the selector may be actuated through a half step because of a change in :polarity during the conditioning periodof a CTC cycle, a cycle of operation is never completed of the selector in response to CTC pulses.

It will be noted that the selector code transmitting apparatus at the control ofiice is so arranged that a selectorcycle cannot be initiated in response to the designation of a code for transmission during a control cycle, particularly because the relay SP is picked up during .a control cycle and because of its being picked up, the pickup circuit for the relay SS is open at back contact 686 :until the cycle is completed. The designation of a selector code for transmission during a control cycle, however, is stored by the selector transmitter 'until the start of a selector :cycle can be initiated at the end of the control cycle as has been heretofore described.

Having thus disclosed a selector calling system as applied to .a specific type of a .C'IlC system as one embodiment of the presentinvention, it is 'to be understood that this form is selected to vfacilitate the disclosure of the present invention rather than to limit the number of forms the invention may assume, and it is to be further understood that various adaptations, alterations and modifications :may be applied to thespecific form shown to meet the requirements of practice, without 'in any manner departing from the spirit or scope of the present invention except as limited by the appending claims.

What I claim is:

'1. In a communication organization in which a pair of line wires connecting a control ofiice and a plurality of field stations is common to a selector calling system and a centralized traflic control system, both of which systems being normally at rest, and the centralized trafiic control system being normally effective to apply energy steadily to -.-said iine wires :of a particular polarity, polarity responsive means at each of the field stations distinctively energized in accordance with the polarity of energization of said line wires, indication cycle initiating means at each of the field stations effective to .initiate an indication cycle by shunting said line wires, said indication cycle initiating means being rendered effective only provided said polarity responsive means at that field station is energized with the polarity applied to said line wires during a period of rest, selector cycle initiating means at the control office effective to initiate the transmission of a selector cycle, said selector cycle initiating means being rendered effective only during a period of rest, and means at the control office responsive to either said indication cycle initiating means or said selector cycle initiating means for pole changing said .l-ine wires to thereby prevent subsequent initiation from other field stations during aconditioning period.

.2. In a communication organization of the character described wherein .a pair .of line wires connecting a control office and .a plurality of field stations is common to .a selector calling system and a centralized traific control system, .both ,of at rest from which they may be initiated into respective cycles of operation, said centralized trafiic control system being effective when both systems are at rest to steadily energize said line wires witha particular polarity, indication transmitting apparatus at each of the field stations, indication cycle initiat ing means at each of the field stations effective to initiate said indication transmitting apparatus into an indication cycle by shunting said line wires, said indication cycle initiating means being rendered effective only during a period of rest, selector transmitting apparatus at the control oflice, selector cycle initiating means at the control effective to initiate said selector transmitting apparatus for the transmission of a selector cycle, means at the control oilice responsive to either said indication cycle initiating means or said selector cycle initiating means for pole chang ing said line wires to thereby prevent initiation during a conditioning period from other field stations, and means at the control ofiice suppressing the initiation of a selector cycle in case selector and indication cycles are substantially simultaneously initiated.

3. In a communication organization of the character described in which a pair of line wires connects a control ofiice and a plurality of field stations, said line wires being common to a selector calling system and a centralized trafiic control system, both of which systems being active only through operating cycles when initiated, and said centralized traffic control system being normally efiective when inactive to apply energy steadily to said line wires of a particular polarity characterizing a period of rest, indication transmitting apparatus at each of the field stations, indication cycle initiating means at each of the field stations elfective to initiate said indication transmitting apparatus into an indication cycle by shunting said line wires, said indication cycle initiating means being rendered eifective only during said period of rest, selector transmitting apparatus at the control oflice, selector cycle initiating means at the control oifice eifective to initiate said selector transmitting apparatus into a selector cycle by shunting said line wires, said selector cycle initiating means being rendered efiective only during a period of rest, and means at the control office for suppressing the initiation of a selector cycle in case selector and indication cycles are both simultaneously initiated.

4. In a communication organization wherein a selector calling system is superimposed upon a centralized trafiic control system having a pair of line wires connecting a control oifice with a plurality of field stations, indication transmitting apparatus at each of the field stations, selector transmitting apparatus at the control ofiice, initiating means at each of the field stations for initiating said indication transmitting apparatus into a cycle of operation comprising means for shunting the line wires for a relatively long period of time during a conditioning period, initiating means at the control ofiice for initiating said selector transmitting apparatus into a cycle of operation comprising the shunting of the line Wires for a relatively short period of time, and electro-responsive means at the control oilice responsive to the termination of a shunt of said line wires for said relatively long period of time, said electro-responsive means being non-responsive to the termination of the shunt of the line wires applied for said relatively short period of time upon the initiation of a selector cycle, and apparatus at the control ofiice governed by said electro-responsive means effective to suppress the start of a selector cycle at the control office in case an indication cycle has been initiated substantially simultaneously with the initiation of a selector cycle.

5. Ina system for communication over a pair of line wires between a control oflice and a plurality of field stations, the combination with a centralized trafficcontrol system for the communication of indications from the field stations to the control ofiice wherein said centralized traffic control system is normally at rest and is adapted to transmit indications from the respective field stations during respective indication cycles of operation according to groups of stations having indications to transmit, one cycle being transmitted from each station in a group with a relatively short period of rest between cycles, but a relatively longer period of rest being required before another group is initiated, of manually operable means for designating selector codes to be transmitted, a selector code transmitter efiective when initiated to apply selector pulses to said line wires, and electro-responsive means governed jointly by said manually operable means and said centralized trafilc control system for governing the time of initiation of said selector transmitter subsequent to the designation of a selector code for transmission, said electroresponsive means being efiective to initiate said selector code transmitter when a period of rest has prevailed greater than the period of rest between indication cycles of any one group but shorter than the period of rest required to initiate another group of indication cycles.

6. A communication organization in which a pair of line wires connect a control ofiice and a plurality of field stations comprising in combination, normally inactive centralized trafiic control transmitting and receiving apparatus at the control ofiice and at the field stations operable when rendered active to transmit respective control and indication cycles of pulses, selector calling transmitting apparatus at the control oifice inductively coupled to said line Wires and effective when rendered active to transmit a selector cycle comprising alternate positive and negative pulses, manually operable means for initiating a cycle of operation of said centralized trafiic control transmitting apparatus, manually operable means for initiating a cycle of operation of said selector transmitting apparatus, storage means responsive to said manually operable means initiating a cycle of operation of said centralized traffic control transmitting apparatus for delaying the actual start of that cycle in case said line wires are being used for the transmission of a selector calling cycle, and storage means at the control ofiice responsive to said means for initiating a cycle of operation of said selector calling transmitting apparatus for delaying the start of that cycle in case said line wires are being used for transmission of control or indication cycles by said centralized tramc control apparatus until a predetermined time subsequent to the restoration of said centralized traffic control apparatus to its normally inactive condition.

'7. In a communication organization of the character described in which a single pair of line wires connecting a control ofiice and a plurality of field stations is common to centralized traiiic control and selector calling systems which are both normally at rest, selector communication apparatus at the control ofiice, comprising in combination, manually operable means for designating selector calling codes for transmission, a selector calling transmitter inductively coupled to said line wires and eiTective when rendered active to transmit a selector cycle comprising alternate positive and negative pulses selected by said manually operable means, and electroresponsive means governed jointly by said manually operable means and said centralized traffic control system for governing the time of rendering said selector calling transmitter active for the application of selector pulses to said line wires in accordance with each manually designated selector code, said electro-responsive means being effective to render said selector calling transmitter active for the transmission of a prior designated selector code at the end of a cycle of said centralized traflic control system upon the termination of a predetermined period of rest subsequent to the use of said line wires by said centralized trafiic control system.

8. In a communication organization wherein a pair of line wires connecting a control oifice and a plurality of field stations is common to centralized traific control and selector calling systems which are both normally inactive, selector calling apparatus at the control ofiice comprising in combination, manually operable means for designating selector calling codes for transmission, a selector calling code transmitter inductively coupled to said line wires and effective when rendered active to transmit a selector calling cycle comprising alternate positive and negative pulses as selected by the actuation of said manually operable means, and electro-responsive means governed jointly by said centralized traffic control system, and said manually operable means for rendering said selector calling code transmitter active to apply a selected code of pulses to said line wires in response to the actuation of said manually operable means only at a time when said centralized trafiic control system is inactive, said electro-responsive means being effective to store the initiation of said selector code transmitter until said centralized trafiic control system has become inactive for a predetermined time interval if said manually operable means is actuated at a time when said centralized traflic control system is active.

9. In a communication organization in which a pair of line Wires connecting a control ofiice and a plurality of field stations is common to both a selector calling system and a centralized traffic control system, said centralized trafilc control system being normally at rest and having indication transmitting apparatus at the respective field stations adapted to transmit indication cycles of operation, one station transmitting at a time, from respective field stations according to groups of stations having indications to transmit, said indication transmitting apparatus permitting only one cycle to be transmitted from each station in a first group with a relatively short period of rest between cycles, but said indication transmitting apparatus permitting another group of cycles to be initiated only after a relatively long period of rest following the first group, manually operable means for designating selector codes to be transmitted, a selector code transmitter effective when rendered active to apply selector pulses to said line wires, and electro-responsive means governed jointly by said manually operable means and said centralized traffic control system for governing the time of initiation of said selector transmitter subsequent to the designation of a selector coding for transmission, said electro-responsive means being effective to initiate said selector code transmitter to apply selector pulses to said line circuit only after a period of rest of the centralized traffic control system has prevailed for a period of time greater than the period of rest between indication cycles within any one of said groups of cycles.

WILLIAM A. BARKER.

REFERENCES CITED The following references are of record in the file of this \patent:

UNITED STATES PATENTS Number Name Date 1,986,026 Suren Jan. 1, 1935 2,399,734 Hailes May 7, 1946 

